A polymer electrolyte fuel cell is required to be operated under low or no humidity conditions with a low relative humidity of reaction gas (fuel gas and oxidant gas) in order to simplify the fuel cell system or to reduce costs.
As an electrolyte material for a catalyst layer to present a membrane/electrode assembly for a polymer electrolyte fuel cell excellent in the power generation characteristics in low or no humidity conditions, the following one has been proposed.
An electrolyte material made of a polymer having a unit (A) which has two ion exchange groups and in which all hydrogen atoms (excluding H+ of the ion exchange groups) bonded to carbon atoms are substituted by fluorine atoms, and a unit (B) which has a 5-membered ring and in which all hydrogen atoms bonded to carbon atoms are substituted by fluorine atoms (Patent Document 1).
However, a catalyst layer containing such an electrolyte material has a problem such that it is hard and brittle and thus is susceptible to cracking, as compared with a catalyst layer containing a conventional electrolyte material which has been commonly used and which is made of a polymer having a unit which has one ion exchange group and in which all hydrogen atoms (excluding H+ of the ion exchange groups) bonded to carbon atoms are substituted by fluorine atoms, and a unit derived from tetrafluoroethylene (hereinafter referred to as TFE).